Metallic magnesium exhibits properties. Magnesium is an important metal for industry and human life

Magnesium is a silvery-white shiny metal, relatively soft and ductile, a good conductor of heat and electricity. Almost 5 times lighter than copper, 4.5 times lighter than iron; even aluminum is 1.5 times heavier than magnesium. Magnesium melts at a temperature of 651 ° C, but under normal conditions it is rather difficult to melt it: heated in air to 550 ° C, it flares up and instantly burns out with a dazzling flame. It is easy to light a strip of magnesium foil with an ordinary match, and in an atmosphere of chlorine, magnesium ignites spontaneously even at room temperature. When magnesium burns, a lot of ultraviolet rays and heat are released - in order to heat a glass of ice water to a boil, you need to burn only 4 g of magnesium.

Magnesium is located in the main subgroups of the second group of the D.I. Mendeleev. Its serial number is 12, its atomic weight is 24.312. The electronic configuration of the magnesium atom in the unexcited state 1S 2 2S 2 P 6 3S 2; electrons of the outer layer are valence, in accordance with this magnesium exhibits valence II. In close connection with the structure of the electron shells of the magnesium atom is its reactivity. Due to the presence of only two electrons on the outer shell, the magnesium atom is inclined to give them up easily to obtain a stable eight-electron configuration; therefore magnesium is chemically very active.

In air, magnesium oxidizes, but the oxide film formed during this protects the metal from further oxidation. The normal electronic potential of magnesium in an acidic medium is -2.37V, in an alkaline medium - 2.69V. In dilute acids, magnesium dissolves already in the cold. It is insoluble in hydrofluoric acid due to the formation of a film of MgF 2 fluoride, which is hardly soluble in water; it is almost insoluble in concentrated sulfuric acid. Magnesium dissolves easily when exposed to solutions of ammonium salts. Alkali solutions have no effect on it. Magnesium is supplied to laboratories in the form of powder or tape. If you set fire to a magnesium tape, then it quickly burns out with a blinding flash, developing a high temperature. Magnesium flashes are used in photography, in the manufacture of illuminating rockets. The boiling point of magnesium is 1107 about C, density \u003d 1.74 g / cm 3, the radius of the atom is 1.60 nm.

Chemical properties of magnesium.

The chemical properties of magnesium are quite peculiar. It easily takes oxygen and chlorine from most elements, is not afraid of caustic alkalis, soda, kerosene, gasoline and mineral oils. Magnesium almost does not interact with cold water, but when heated, it decomposes with the release of hydrogen. In this respect, it occupies an intermediate position between beryllium, which does not react with water at all, and calcium, which easily interacts with it. The reaction is especially intense with water vapor heated above 380 ° C:

Mg 0 (tv) + H 2 + O (gas) Mg +2 O (tv) + H 2 0 (gas).

Since the product of this reaction is hydrogen, it is clear that extinguishing burning magnesium with water is unacceptable: the formation of an explosive mixture of hydrogen with oxygen and an explosion can occur. Burning magnesium and carbon dioxide cannot be extinguished: magnesium reduces it to free carbon -4e

2Mg 0 + C +4 O 2 2Mg +2 O + C 0,

You can stop oxygen access to burning magnesium by covering it with sand, although magnesium also interacts with silicon oxide (IV), but with much less heat release:

2Mg 0 + Si +4 O 2 \u003d 2Mg +2 O + Si 0

this determines the possibility of using sand for quenching silicon. The danger of magnesium ignition during intense heating is one of the reasons why its use as a technical material is limited.

In the electrochemical series of voltages, magnesium is much to the left of hydrogen and actively reacts with dilute acids to form salts. Magnesium has some peculiarities in these reactions. It does not dissolve in hydrofluoric, concentrated sulfuric and in a mixture of sulfuric and nitric acids, which dissolves other metals almost as effectively as "aqua regia" (a mixture of HCl and HNO 3). The resistance of magnesium to dissolution in hydrofluoric acid is simply explained: the surface of magnesium is covered with a film of magnesium fluoride MgF 2, insoluble in hydrofluoric acid. The stability of magnesium to sufficiently concentrated sulfuric acid and its mixture with nitric acid is more difficult to explain, although in this case the reason lies in the passivation of the magnesium surface. Magnesium practically does not interact with solutions of alkalis and ammonium hydroxide.

There is no surprise in this reaction. This reaction is essentially the same as the reaction of displacing hydrogen from acids by metals. In one definition, an acid is a substance that dissociates to form hydrogen ions.

When magnesium is heated in a halogen atmosphere, ignition occurs and the formation of halide salts.

The cause of the ignition is a very high heat release, as in the case of the reaction of magnesium with oxygen. So when 1 mol of magnesium chloride is formed from magnesium and chlorine, 642 KJ is released. When heated, magnesium combines with sulfur (MgS) and nitrogen (Mg 3 N 2). Under elevated pressure and heating with hydrogen, magnesium forms magnesium hydride

The high affinity of magnesium for chlorine made it possible to create a new metallurgical production - "magnesiumthermia" - the production of metals as a result of the reaction

MeCln + 0.5nMg \u003d Me + 0.5nMgCl 2

this method produces metals that play a very important role in modern technology - zirconium, chromium, thorium, beryllium. Lightweight and durable "space age metal" - almost all titanium is obtained in this way.

The essence of the production boils down to the following: when obtaining metallic magnesium by electrolysis of a magnesium chloride melt, chlorine is formed as a by-product. This chlorine is used to obtain titanium (IV) chloride TiCl 4, which is reduced by magnesium to titanium metal

Ti +4 Cl 4 + 2Mg 0 Ti 0 + 2Mg +2 Cl 2

The resulting magnesium chloride is reused for the production of magnesium, etc. Titanium-magnesium plants operate on the basis of these reactions. Along the way, with titanium and magnesium, other products are obtained, such as berthollet's salt KClO 3, chlorine, bromine, and products - fibrolite and xylite boards, which will be discussed below. In such a complex production, the degree of use of raw materials, the profitability of production is high, and the mass of waste is not large, which is especially important for protecting the environment from pollution.

FIELDS OF MAGNESIUM APPLICATION.

Magnesium is used in the form of metal plates for corrosion protection of ships and pipelines. The protective effect of the magnesium "protector" is due to the fact that an electric circuit is created from a steel structure and a magnesium protector (magnesium is to the left in the electrochemical series of voltages than iron). The magnesium protector is destroyed; the main steel part of the structure is preserved. In metallurgy, magnesium is used as a "deoxidizer" - a substance that binds harmful impurities in the iron melt. The addition of 0.5% magnesium to cast iron greatly increases the ductility of the cast iron and its tensile strength. Magnesium is also used in the manufacture of some electrochemical cells.

Magnesium alloys play a very important role in technology. There is a whole family of magnesium alloys with the general name "electron". They are based on magnesium in combination with aluminum (10%), zinc (up to 5%), manganese (1-2%). Small additions of other metals impart various valuable properties to the "electron". But the main property of all types of "electrons" is their lightness (1.8 g / cm 3) and excellent mechanical properties. They are used in those branches of technology where lightness is especially highly valued: in aircraft and rocketry. AT last years new air-stable magnesium-lithium alloys with very low density (1.35 g / cm 3) have been created. Their use in technology is very promising. Magnesium alloys are priced not only because of their lightness. Their heat capacity is 2-2.5 times higher than that of steel. Equipment made of magnesium alloys heats up less than steel. An aluminum alloy with a high magnesium content (5-30%) is also used. This "magnalite" alloy is harder and stronger than aluminum, easier to process and polish. The number of metals with which magnesium forms alloys is large. From the diagram illustrating the Hume-Rothery rule, it is clear that magnesium does not mix in the melt with its neighbor, beryllium, which is close in position in the periodic table. Due to the strong difference in interatomic distances, it does not form alloys with magnesium either with iron.

Among oxygen compounds of Mg, it is necessary to note magnesium oxide MgO, also called burnt magnesia. It is used in the manufacture of refractory bricks, because its melting point is 2800 ° C. Burnt magnesia is also used in medical practice.

Magnesium silicates are of interest - talc 3MgO * 4SiO 2 * H 2 O and asbestos CaO * MgO * 4SiO 2, which have high fire resistance. Asbestos has a fibrous structure, so it can be spun and made into overalls for working at high temperatures. Magnesium carbonates and silicates are insoluble in water.

Interest in magnesium and alloys based on it is due, on the one hand, to a combination of properties important for practical use, and, on the other hand, to large raw materials of magnesium. The scope of using magnesium and magnesium alloys with special chemical properties is wide, for example, in power supplies and for protectors for protecting steel structures from corrosion.

In the CIS, as well as abroad, there are large reserves of magnesium mineral raw materials, which are convenient for its extraction. These are deposits of solid salts containing magnesium, as well as brines from a number of salt lakes. In addition, magnesium can be extracted from seawater. Thus, magnesium does not face the problem of depletion of raw materials, which is becoming increasingly important for many other industrially important metals. Although magnesium is one of the main industrial metals, its production continues to be significantly inferior to the production of aluminum and steel.

An examination of its production and consumption in the developed capitalist and developing countries provides a definite orientation in the needs of industry for magnesium. After the Second World War and up to the beginning of the 70s of the XX century, there was a continuous growth in the production and consumption of magnesium, then its stabilization took place. The largest producer of magnesium in the capitalist countries is the United States, whose share in total production is slightly more than 50%.

Structural magnesium alloys are just one, and not the largest in terms of volume, area of \u200b\u200bmagnesium application. Magnesium is widely used as a chemical reagent in many metallurgical processes. In particular, it is used in ferrous metallurgy for the treatment of cast iron for desulfurization. In general, in recent years, there has been a trend towards an increase in the use of magnesium as a chemical reagent. A significant amount of magnesium is used to obtain titanium, and it is necessary to look for ways to increase the efficiency of its use for these purposes. There is also a significant interest in magnesium and its alloys as hydrogen accumulators.

There is a certain bias against magnesium alloys on the part of consumers with regard to their fire hazard, low corrosion resistance, and increased sensitivity to stress concentrators. This prejudice must be overcome. At the same time, work should be continued aimed at improving the performance characteristics of magnesium alloys, in particular, increasing their corrosion resistance.

Magnesium is a metal widespread in nature and of great biogenic importance for humans. It is an integral part of a large number of various minerals, sea water, hydrothermal waters.

Properties

Silvery shiny metal, very light and ductile. Non-magnetic, has high thermal conductivity. Under normal conditions in air, it becomes covered with an oxide film. When heated above 600 ° C, the metal burns with the release of a large amount of heat and light. It burns in carbon dioxide and reacts actively with water, so it is useless to extinguish it using traditional methods.

Magnesium does not interact with alkalis, reacts with acids with the release of hydrogen. Resistant to halogens and their compounds; for example, it does not interact with fluorine, hydrofluoric acid, dry chlorine, iodine, bromine. Does not collapse under the influence of petroleum products. Magnesium is not resistant to corrosion; this drawback is corrected by adding small amounts of titanium, manganese, zinc, zirconium to the alloy.

Magnesium is essential for the health of the cardiovascular and nervous systems, for the synthesis of proteins and the absorption of glucose, fats and amino acids by the body. Magnesium orotate (vitamin B13) plays an important role in metabolism, normalizes cardiac activity, prevents the deposition of cholesterol on the walls of blood vessels, increases the efficiency of the body of athletes, not inferior in effectiveness to steroid drugs.

Magnesium is obtained in various ways, from natural minerals and sea water.

Application

Most of the extracted magnesium is used for the production of magnesium structural alloys, which are in demand in the aviation, automotive, nuclear, chemical, oil refining industries, and in instrument making. Magnesium alloys are characterized by lightness, strength, high specific stiffness, and good machinability. They are non-magnetic, excellent at dissipating heat, and have 20 times higher vibration resistance than alloy steel. Magnesium alloys are used for the manufacture of tanks for the storage of gasoline and oil products, parts of nuclear reactors, jackhammers, pneumatic tubes, cars; tanks and pumps for working with hydrofluoric acid, for storing bromine and iodine; cases of laptops and cameras.
- Magnesium is widely used to obtain some metals by reduction (vanadium, zirconium, titanium, beryllium, chromium, etc.); to give steel and cast iron better mechanical properties, for cleaning aluminum.
- In its pure form, it is part of many semiconductors.
- In the chemical industry, powdered magnesium is used for drying organic matter, for example, alcohol, aniline. Organomagnesium compounds are used in complex chemical synthesis (for example, to obtain vitamin A).
- Magnesium powder is in demand in rocketry as a high-calorific fuel. In military affairs - in the production of illuminating rockets, tracer ammunition, incendiary bombs.
- Pure magnesium and its compounds are used for the manufacture of chemical powerful current sources.
- Magnesium oxide is used for the manufacture of crucibles and metallurgical furnaces, refractory bricks, in the manufacture of synthetic rubber.
- Crystals of magnesium fluoride are in demand in optics.
- Magnesium hydride is a solid powder containing a large percentage of hydrogen, which can be easily obtained by heating. The substance is used as a "storage" for hydrogen.
“Now less often, but before, magnesium powder was widely used in chemical flashlights.
- Magnesium compounds are used for bleaching and etching fabrics, for the manufacture of heat-insulating materials, special types of bricks.
- Magnesium is a part of many medicines, both internal and external (bischofite) use. It is used as an anticonvulsant, laxative, sedative, cardiac, antispasmodic, to regulate the acidity of gastric juice, as an antidote for acid poisoning, as a disinfectant for the stomach, to treat injuries and joints.
- Magnesium stearate is used in the pharmaceutical and cosmetic industry as a filler for tablets, powders, creams, eye shadows; in the food industry it is used as a food additive E470, which prevents caking of products.

In the chemical store "PrimeChemicalsGroup" you can buy chemical magnesium and its various compounds - magnesium stearate, bischofite magnesium chloride, magnesium carbonate and others, as well as a wide range of chemical reagents, laboratory glassware and other goods for laboratories and production. You will like the prices and level of service!

Magnesium compounds have been known to man for a very long time. Magnesite (in Greek Magnhsia oliqV) was a soft, white, soapy mineral (soapstone, or talc) found in the Magnesia region of Thessaly. When this mineral was calcined, a white powder was obtained, which became known as white magnesia.

In 1695 N. Gro, evaporating the mineral water of the Epsom spring (England), obtained salt, which had a bitter taste and laxative effect (MgSO 4 · 7H 2 O). A few years later, it turned out that when interacting with soda or potash, this salt forms a white loose powder, the same one that is formed when magnesite is calcined.

In 1808, the English chemist and physicist Humphrey Davy, by electrolysis of slightly moistened white magnesia with mercury oxide as a cathode, obtained an amalgam of a new metal capable of forming white magnesia. They called it magnesium. Davy obtained the contaminated metal, and pure magnesium was isolated only in 1829 by the French chemist Bussy Antoine (1794–1882).

Distribution of magnesium in nature and its industrial extraction.

Magnesium is found in crystalline rocks in the form of insoluble carbonates or sulfates, and (in a less accessible form) in the form of silicates. The assessment of its total content depends significantly on the geochemical model used, in particular, on the weight ratios of volcanic and sedimentary rocks. Values \u200b\u200bfrom 2 to 13.3% are currently used. Perhaps the most acceptable value is 2.76%, which ranks magnesium in sixth place after calcium (4.66%), over sodium (2.27%) and potassium (1.84%).

Large land areas such as the Dolomites in Italy are composed primarily of the dolomite mineral MgCa (CO 3) 2. There are also sedimentary minerals magnesite MgCO 3, epsomite MgSO 4 · 7H 2 O, carnallite K 2 MgCl 4 · 6H 2 O, langbeinite K 2 Mg 2 (SO 4) 3.

There are dolomite deposits in many other areas, including the Moscow and Leningrad regions. Rich deposits of magnesite have been found in the Middle Urals and in the Orenburg region. In the area of \u200b\u200bSolikamsk, a largest deposit carnallite. Magnesium silicates are represented by the basalt mineral olivine (Mg, Fe) 2 (SiO 4), soapstone (talc) Mg 3 Si 4 O 10 (OH) 2, asbestos (chrysotile) Mg 3 Si 2 O 5 (OH) 4 and mica. Spinel MgAl 2 O 4 belongs to precious stones.

A large amount of magnesium is found in the waters of the seas and oceans and in natural brines ( cm... CHEMISTRY OF HYDROSPHERE). In some countries, they are the raw material for obtaining magnesium. It is second only to sodium in terms of the content of metallic elements in seawater. Each cubic meter of sea water contains about 4 kg of magnesium. Magnesium is also present in fresh water, causing, along with calcium, its hardness.

Magnesium is always found in plants, as it is part of chlorophylls.

Characterization of a simple substance and industrial production of metallic magnesium.

Magnesium is a silvery-white lustrous metal, relatively soft, ductile and malleable. Its strength and hardness are minimal in prevalence for cast specimens, higher for pressed specimens.

Under normal conditions, magnesium is resistant to oxidation due to the formation of a strong oxide film. However, it actively reacts with most non-metals, especially when heated. Magnesium ignites in the presence of halogens (in the presence of moisture), forming the corresponding halides, and burns with a dazzling flame in air, turning into oxide MgO and nitride Mg 3 N 2:

2Mg (q) + O 2 (g) \u003d 2MgO (q); DG ° \u003d –1128 kJ / mol

3Mg (q) + N 2 (t) \u003d Mg 3 N 2 (q); DG ° \u003d –401 kJ / mol

Despite the low melting point (650 ° C), it is impossible to melt magnesium in air.

When exposed to hydrogen under a pressure of 200 atm at 150 ° C, magnesium forms the hydride MgH 2. Magnesium does not react with cold water, but displaces hydrogen from boiling water and forms hydroxide Mg (OH) 2:

Mg + 2H 2 O \u003d Mg (OH) 2 + H 2

At the end of the reaction, the pH value (10.3) of the resulting saturated solution of magnesium hydroxide corresponds to the equilibrium:

In the latter case, the resulting mixture of carbon monoxide and magnesium vapor must be rapidly cooled with an inert gas to prevent a reverse reaction.

The world production of magnesium is approaching 400 thousand tons per year. The main producers are the USA (43%), the CIS countries (26%) and Norway (17%). In recent years, China has been sharply increasing the export of magnesium. In Russia, one of the largest magnesium producers is the titanium-magnesium plant in Berezniki (Perm region) and the Solikamsk magnesium plant. Magnesium production is also being developed in Asbestos.

Magnesium is the lightest structural material used in industrial scale... Its density (1.7 g cm –3) is less than two thirds of that of aluminum. Magnesium alloys weigh four times less than steel. In addition, magnesium is excellently processed and can be cast and reworked by any standard metalworking methods (rolling, stamping, drawing, forging, welding, brazing, riveting). Therefore, its main field of application is as a lightweight structural metal.

Magnesium alloys usually contain more than 90% magnesium, as well as 2-9% aluminum, 1-3% zinc and 0.2-1% manganese. The retention of strength at high temperatures (up to 450 ° C) is noticeably improved when alloyed with rare earth metals (for example, praseodymium and neodymium) or thorium. These alloys can be used for car engine casings as well as aircraft fuselages and landing gear. Magnesium is used not only in aviation, but also for the manufacture of stairs, dock walkways, cargo platforms, conveyors and lifts, as well as in the manufacture of photographic and optical equipment.

Up to 5% magnesium is added to industrial aluminum to improve mechanical properties, weldability and corrosion resistance. Magnesium is also used for the cathodic protection of other metals from corrosion, as an oxygen scavenger and a reducing agent in the production of beryllium, titanium, zirconium, hafnium, and uranium. Mixtures of magnesium powder with oxidants are used in pyrotechnics for the preparation of lighting and incendiary compositions.

Magnesium compounds.

The predominant oxidation state (+2) for magnesium is due to its electronic configuration, ionization energies, and atomic size. The oxidation state (+3) is impossible, since the third ionization energy for magnesium is 7733 kJ mol –1. This energy is much higher than can be compensated by the formation of additional bonds, even if they are predominantly covalent. The reasons for the instability of magnesium compounds in the oxidation state (+1) are less obvious. Estimation of the enthalpy of formation of such compounds shows that they must be stable with respect to their constituent elements. The reason that magnesium (I) compounds are not stable is the much higher value of the enthalpy of formation of magnesium (II) compounds, which should lead to rapid and complete disproportionation:

Mg (q) + Cl 2 (g) \u003d MgCl 2 (q);

D H° sample \u003d –642 kJ / (mol MgCl 2)

2Mg (q) + Cl 2 (g) \u003d 2MgCl (q);

D H° sample \u003d –250 kJ / (2 mol MgCl)

2MgCl (q) \u003d Mg (q) + MgCl 2 (q);

D H° disproportion \u003d -392 kJ / (2 mol MgCl)

If a synthetic route is found that makes disproportionation difficult, such compounds may be obtained. There is some evidence for the formation of magnesium (I) particles during electrolysis on magnesium electrodes. So, during the electrolysis of NaCl, hydrogen is released on the magnesium anode, and the amount of magnesium lost by the anode corresponds to a charge of +1.3. Similarly, in the electrolysis of an aqueous solution of Na 2 SO 4, the amount of released hydrogen corresponds to the oxidation of water by magnesium ions, the charge of which corresponds to +1.4.

Most magnesium salts are highly soluble in water. The dissolution process is accompanied by minor hydrolysis. The resulting solutions have a weakly acidic environment:

2+ + H 2 O + + H 3 O +

Magnesium compounds with many non-metals, including carbon, nitrogen, phosphorus, sulfur, are irreversibly hydrolyzed by water.

Magnesium hydride composition MgH 2 is a polymer with bridging hydrogen atoms. The coordination number of magnesium in it is 4. This structure leads to a sharp decrease in the thermal stability of the compound. Magnesium hydride is easily oxidized by atmospheric oxygen and water. These reactions are accompanied by a large release of energy.

Magnesium nitride Mg 3 N 2. Forms yellowish crystals. The hydrolysis of magnesium nitride produces ammonia hydrate:

Mg 3 N 2 + 8H 2 O \u003d 3Mg (OH) 2 + 2NH 3 · H 2 O

If the hydrolysis of magnesium nitride is carried out in an alkaline medium, ammonia hydrate is not formed, but gaseous ammonia is released. Hydrolysis in an acidic environment leads to the formation of magnesium and ammonium cations:

Mg 3 N 2 + 8H 3 O + \u003d 3Mg 2+ + 2NH 4 + + 8H 2 O

Magnesium oxide MgO is called burnt magnesia. It is obtained by calcining magnesite, dolomite, basic magnesium carbonate, magnesium hydroxide, as well as calcining bischofite MgCl 2 6H 2 O in an atmosphere of water vapor.

The reactivity of magnesium oxide depends on the temperature of its production. Magnesium oxide prepared at 500–700 ° C is called light magnesia. It easily reacts with dilute acids and water to form the corresponding salts or magnesium hydroxide, and absorbs carbon dioxide and moisture from the air. Magnesium oxide obtained at 1200–1600 ° C is called heavy magnesia. It is acid and water resistant.

Magnesium oxide is widely used as a heat-resistant material. It is distinguished by both high thermal conductivity and good electrical insulating properties. Therefore, this connection is used in insulating radiators for local heating.

Lighter grades of magnesia are used to prepare magnesia cement and building materials on its basis, and also as a vulcanizing agent in the rubber industry.

Magnesium hydroxide Mg (OH) 2 forms colorless crystals. The solubility of this compound is low (2 · 10 –4 mol / L at 20 ° C). It can be converted into solution by the action of ammonium salts:

Mg (OH) 2 + 2NH 4 Cl \u003d MgCl 2 + 2NH 3 H 2 O

Magnesium hydroxide is thermally unstable and decomposes when heated:

Mg (OH) 2 \u003d MgO + H 2 O

On an industrial scale, magnesium hydroxide is obtained by lime precipitation from sea water and natural brines.

Magnesium hydroxide is a mild base that is widely used in the form of an aqueous solution (magnesia milk) to reduce gastric acidity. At the same time, despite its mildness, Mg (OH) 2 neutralizes acids 1.37 times more than sodium hydroxide NaOH and 2.85 times more than sodium bicarbonate NaHCO 3.

It is also used for the production of magnesium oxide, sugar refining, water purification in boilers, and as a component of toothpastes.

Magnesium carbonate MgCO 3 forms colorless crystals. It occurs naturally in anhydrous form (magnesite). In addition, magnesium carbonate penta-, tri- and monohydrates are known.

The solubility of magnesium carbonate in the absence of carbon dioxide is about 0.5 mg / l. In the presence of an excess of carbon dioxide and water, magnesium carbonate transforms into soluble bicarbonate, and when boiling occurs reverse process... Carbonate and bicarbonate react with acids to release carbon dioxide and form the corresponding salts. When heated, magnesium carbonate, without melting, decomposes:

MgCO 3 \u003d MgO + CO 2

This process is used to produce magnesium oxide. In addition, natural magnesium carbonate is a raw material for the production of metallic magnesium and its compounds. It is also used as fertilizer and to reduce soil acidity.

Loose magnesium carbonate powder is poured between the double walls of the liquid oxygen storage. This insulation is cheap and reliable.

Magnesium sulfate MgSO 4 is known in the anhydrous state as well as in the form of various hydrates. Kieserite MgSO 4 · H 2 O, epsomite MgSO 4 · 7H 2 O and hexahydrate MgSO 4 · 6H 2 O occur in nature.

In medicine, magnesium sulfate heptahydrate MgSO 4 · 7H 2 O, commonly known as English or bitter salt, is used. This compound has a laxative effect. With intramuscular or intravenous infusion, magnesium sulfate relieves convulsive state, reduces vasospasm.

Magnesium sulfate is used in the textile and paper industry as a mordant for dyeing, as well as a weighting agent for cotton and silk and a paper filler. It serves as a raw material for the production of magnesium oxide.

Magnesium nitrate Mg (NO 3) 2 are colorless hygroscopic crystals. Solubility in water at 20 ° C is 73.3 g per 100 g. Hexahydrate crystallizes from aqueous solutions. Above 90 ° C, it is dehydrated to monohydrate. Then water is split off with partial hydrolysis and decomposition to magnesium oxide. This process is used in the synthesis of high purity magnesium oxide. Magnesium nitrate is used to obtain nitrates of other metals, as well as various magnesium compounds. In addition, magnesium nitrate is included in complex fertilizers and pyrotechnic mixtures.

Magnesium perchlorate Mg (ClO 4) 2 forms very hygroscopic colorless crystals. It is readily soluble in water (99.6 g per 100 g) and organic solvents. Hexahydrate crystallizes from aqueous solutions. Concentrated solutions of magnesium perchlorate in organic solvents and its solvates with reducing agent molecules are explosive.

Partially hydrated magnesium perchlorate, containing 2–2.5 water molecules, is marketed under the trade name anhydrone. To obtain anhydrous magnesium perchlorate, it is dried in vacuum at 200-300 ° C. It is used as a gas desiccant. It absorbs not only water vapors, but also ammonia, alcohol vapors, acetone and other polar substances.

Magnesium perchlorate is used as an acylation catalyst for the Friedel - Crafts reaction, and also as an oxidizing agent in microanalysis.

Magnesium fluoride MgF 2 is slightly soluble in water (0.013 g in 100 g at 25 ° C). It occurs naturally in the form of the mineral selaite. Get magnesium fluoride by reacting magnesium sulfate or oxide with hydrofluoric acid or magnesium chloride with potassium or ammonium fluoride.

Magnesium fluoride is a component of fluxes, glasses, ceramics, enamels, catalysts, and mixtures for producing artificial mica and asbestos. Moreover, it is an optical and laser material.

Magnesium chloride MgCl 2 is one of the most industrially important magnesium salts. Its solubility is 54.5 g per 100 g of water at 20 ° C. Concentrated aqueous solutions of magnesium chloride dissolve magnesium oxide. From the obtained solutions MgCl 2 · mMg (OH) 2 · nH 2 O crystallize. These compounds are included in the composition of magnesia cements.

Magnesium chloride forms crystalline hydrates with 1, 2, 4, 6, 8 and 12 water molecules. With increasing temperature, the number of water molecules of crystallization decreases.

In nature, magnesium chloride occurs in the form of bischofite minerals MgCl 2 6H 2 O, chloromagnesite MgCl 2, and also carnallite. It is found in seawater, brine from salt lakes, and some underground brines.

Anhydrous magnesium chloride is used in the production of metallic magnesium and magnesium oxide, and hexahydrate is used to obtain magnesia cements. An aqueous solution of magnesium chloride is used as a refrigerant and antifreeze. It serves as a means against icing airfields of airfields, railway rails and switches, as well as against freezing of coal and ores. The wood is impregnated with a solution of magnesium chloride to give it fire resistance.

Magnesium bromide MgBr 2 is readily soluble in water (101.5 g per 100 g at 20 ° C). From aqueous solutions it crystallizes from -42.7 to 0.83 ° C in the form of decahydrate, at higher temperatures - in the form of hexahydrate. It forms numerous crystal solvates such as MgB 2 6ROH (R \u003d Me, Et, Pr), MgBr 2 6Me 2 CO, MgBr 2 3Et 2 O, as well as MgBr 2 nNH 3 ( n = 2–6).

Complex magnesium compounds... In aqueous solutions, the magnesium ion exists in the form of a 2+ aqua complex. In a non-aqueous solvent, such as liquid ammonia, the magnesium ion forms complexes with the solvent molecules. Magnesium salt solvates usually crystallize from such solutions. Several halide complexes of the MX 4 2– type are known, where X is a halide anion.

Among the complex compounds of magnesium, chlorophylls, which are modified porphyrin complexes of magnesium, are of particular importance. They are vital for photosynthesis in green plants.

Organomagnesium compounds... Numerous compounds containing metal-carbon bonds have been obtained for magnesium. Especially a lot of research is devoted to the Grignard reagents RMgX (X \u003d Cl, Br, I).

Grignard reagents are the most important organometallic magnesium compounds and are probably the most used organometallic reagents. This is due to their ease of production and synthetic versatility. It has been established that in solution these compounds can contain a variety of chemical particles in mobile equilibrium.

Grignard reagents are usually obtained by slowly adding an organic halide to a suspension of magnesium shavings in an appropriate solvent with vigorous stirring and complete absence of air and moisture. The reaction usually starts slowly. It can be initiated by a small iodine crystal that destroys the protective layer on the metal surface.

Grignard reagents are widely used for the synthesis of alcohols, aldehydes, ketones, carboxylic acids, esters and amides and are probably the most important reagents for creating carbon-carbon bonds, as well as bonds between carbon atoms and other elements (nitrogen, oxygen, sulfur, etc. etc.).

Compounds R 2 Mg usually decompose on heating. In the crystalline state, they have the structure of linear polymers with bridging alkyl groups. Compound MgMe 2 is a non-volatile polymer, stable up to ~ 250 ° C, insoluble in hydrocarbons and only slightly soluble in ether. Compound MgEt 2 and higher homologues are very similar to MgMe 2, but they decompose at a lower temperature (175–200 ° С), forming the corresponding alkene and MgH 2 by the reverse reaction of their preparation. MgPh 2 is similar to them; it is insoluble in benzene, dissolves in ether with the formation of the monomeric complex MgPh 2 · 2Et 2 O and decomposes at 280 ° C with the formation of Ph 2 and metallic magnesium.

The biological role of magnesium.

Green leaves of plants contain chlorophylls, which are magnesium-containing porphyrin complexes involved in photosynthesis.

Magnesium is also closely involved in biochemical processes in animal organisms. Magnesium ions are necessary for the initiation of enzymes responsible for the conversion of phosphates, for the transfer of nerve impulses and for the metabolism of carbohydrates. They are also involved in muscle contraction that is initiated by calcium ions.

Several years ago, scientists at the University of Minnesota in the United States found that eggshells are stronger the more they contain magnesium.

An adult body weighing 65 kg contains about 20 g of magnesium (mainly in the form of ions). Most of it is concentrated in the bones. The intracellular fluid contains complexes of magnesium with ATP and ADP.

The daily requirement for this element is 0.35 g. With a monotonous diet, a lack of green vegetables and fruits, as well as alcoholism, magnesium deficiency often occurs. Apricots, peaches and cauliflower are especially high in magnesium. It is also found in ordinary cabbage, potatoes, tomatoes.

Statistics say that residents of areas with a warmer climate have spasms of blood vessels less often than northerners. It is believed that the reason for this is the eating habits in cold regions. They eat fewer fruits and vegetables, which means they get less magnesium.

Studies by French biologists have shown that tired people have less magnesium in their blood than those who have rested. It is believed that a diet rich in magnesium should help doctors fight such a serious ailment as overwork.

Elena Savinkina

DEFINITION

Magnesium - the twelfth element of the Periodic Table. Designation - Mg from the Latin "magnesium". Located in the third period, IIA group. Refers to metals. The nuclear charge is 12.

Magnesium is abundant in nature. It occurs in large quantities in the form of magnesium carbonate, forming minerals magnesite MgCO 3 and dolomite MgCO 3 × CaCO 3. Magnesium sulfate and chloride are part of the minerals KCl × MgSO 4 × 3H 2 O and carnallite KCl × MgCl 2 × 6H 2 O. The Mg 2+ ion is contained in seawater, imparting a bitter taste to it. The total amount of magnesium in the earth's crust is about 2% (mass.).

As a simple substance, magnesium is a silvery white (Fig. 1), a very light metal. In air, it changes little, since it quickly becomes covered with a thin layer of oxide, which protects it from further oxidation.

Figure: 1. Magnesium. Appearance.

Atomic and molecular weight of magnesium

The relative molecular weight of a substance (M r) is a number that shows how many times the mass of a given molecule is more than 1/12 of the mass of a carbon atom, and the relative atomic mass of an element (Ar) is how many times the average mass of atoms of a chemical element is more than 1/12 mass of a carbon atom.

Since in the free state magnesium exists in the form of monatomic Mg molecules, the values \u200b\u200bof its atomic and molecular masses coincide. They are equal to 24.304.

Magnesium isotopes

It is known that in nature magnesium can be found in the form of three stable isotopes 24 Mg (23.99%), 25 Mg (24.99%) and 26 Mg (25.98%). Their mass numbers are 24, 25 and 26, respectively. The nucleus of the magnesium isotope 24 Mg contains twelve protons and twelve neutrons, and the isotopes 25 Mg and 26 Mg contain the same number of protons, thirteen and fourteen neutrons, respectively.

There are artificial isotopes of magnesium with mass numbers from 5 to 23 and from 27 to 40.

Magnesium ions

At the external energy level of the magnesium atom, there are two electrons, which are valence:

1s 2 2s 2 2p 6 3s 2.

As a result of chemical interaction, manias donate their valence electrons, i.e. is their donor, and turns into a positively charged ion:

Mg 0 -2e → Mg 2+.

Molecule and atom of magnesium

In a free state, magnesium exists in the form of monatomic Mg molecules. Here are some properties that characterize the atom and molecule of magnesium:

Magnesium alloys

The main field of application of metallic magnesium is the production of various light alloys on its basis. The addition of small amounts of other metals to magnesium dramatically changes its mechanical properties, imparting significant hardness, strength and corrosion resistance to the alloy.

Alloys called electrons have especially valuable properties. They belong to three systems: Mg-Al-Zn, Mg-Mn and Mg-Zn-Zr. The most widely used are alloys of the Mg-Al-Zn system containing from 3 to 10% aluminum and from 0.2 to 3% zinc. The advantage of magnesium alloys is their low density (about 1.8 g / cm 3).

Examples of problem solving

EXAMPLE 1

Group IIA contains only metals - Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium) and Ra (radium). The chemical properties of the first representative of this group, beryllium, are most different from the chemical properties of the rest of the elements of this group. Its chemical properties are in many ways even more similar to aluminum than to the rest of Group IIA metals (the so-called "diagonal similarity"). Magnesium also differs markedly from Ca, Sr, Ba and Ra in chemical properties, but it still has much more similar chemical properties with them than with beryllium. Due to the significant similarity of the chemical properties of calcium, strontium, barium and radium, they are combined into one family, called alkaline earth metals.

All elements of the IIA group belong to s-elements, i.e. contain all their valence electrons on s-sub-level. Thus, the electronic configuration of the outer electron layer of all chemical elements of a given group has the form ns 2 where n - number of the period in which the element is located.

Due to the peculiarities of the electronic structure of group IIA metals, these elements, in addition to zero, are capable of having only one single oxidation state equal to +2. Simple substances formed by the elements of group IIA, with participation in any chemical reactions, can only be oxidized, i.e. donate electrons:

Ме 0 - 2e - → Ме +2

Calcium, strontium, barium and radium are extremely reactive. The simple substances formed by them are very strong reducing agents. Magnesium is also a powerful reducing agent. The reducing activity of metals obeys the general laws of the periodic law of D.I. Mendeleev and increases down the subgroup.

Interaction with simple substances

with oxygen

Without heating, beryllium and magnesium do not react with either atmospheric oxygen or pure oxygen due to the fact that they are covered with thin protective films consisting of BeO and MgO oxides, respectively. Their storage does not require any special methods of protection from air and moisture, in contrast to alkaline earth metals, which are stored under a layer of a liquid inert to them, most often kerosene.

Be, Mg, Ca, Sr when burning in oxygen form oxides of the composition MeO, and Ba - a mixture of barium oxide (BaO) and barium peroxide (BaO 2):

2Mg + O 2 \u003d 2MgO

2Ca + O 2 \u003d 2CaO

2Ba + O 2 \u003d 2BaO

Ba + O 2 \u003d BaO 2

It should be noted that during the combustion of alkaline earth metals and magnesium in air, the reaction of these metals with nitrogen in the air also occurs as a side effect, as a result of which, in addition to compounds of metals with oxygen, nitrides are also formed with the general formula Me 3 N 2.

with halogens

Beryllium reacts with halogens only at high temperatures, and the rest of the IIA group metals already at room temperature:

Mg + I 2 \u003d MgI 2 - magnesium iodide

Ca + Br 2 \u003d CaBr 2 - calcium bromide

Ba + Cl 2 \u003d BaCl 2 - barium chloride

with non-metals of IV-VI groups

All Group IIA metals react when heated with all Group IV – VI nonmetals, but depending on the position of the metal in the group, as well as the activity of the nonmetals, a different degree of heating is required. Since beryllium is the most chemically inert among all IIA metals, when carrying out its reactions with non-metals, it is required to significantly abouthigher temperature.

It should be noted that the reaction of metals with carbon can form carbides of different nature. Distinguish between carbides belonging to methanides and conventionally considered derivatives of methane, in which all hydrogen atoms are replaced by metal. They, like methane, contain carbon in the oxidation state -4, and during their hydrolysis or interaction with non-oxidizing acids, one of the products is methane. There is also another type of carbides - acetylenides, which contain the C 2 2- ion, which is actually a fragment of the acetylene molecule. Carbides of the acetylenide type upon hydrolysis or interaction with non-oxidizing acids form acetylene as one of the reaction products. What type of carbide - methanide or acetylenide - is obtained by the interaction of a particular metal with carbon depends on the size of the metal cation. Methanides, as a rule, are formed with metal ions with a small radius, and acetylenides with ions of a larger size. In the case of metals of the second group, methanide is obtained by the interaction of beryllium with carbon:

The rest of the II A group metals form acetylenides with carbon:

Group IIA metals form silicides with silicon - compounds of the Me 2 Si type, with nitrogen - nitrides (Me 3 N 2), phosphorus - phosphides (Me 3 P 2):

with hydrogen

All alkaline earth metals react with hydrogen when heated. In order for magnesium to react with hydrogen, heating alone, as in the case of alkaline earth metals, is not enough; in addition to high temperature, an increased pressure of hydrogen is also required. Beryllium does not react with hydrogen under any conditions.

Interaction with complex substances

with water

All alkaline earth metals actively react with water to form alkalis (soluble metal hydroxides) and hydrogen. Magnesium reacts with water only when boiling due to the fact that when heated, the protective oxide film of MgO dissolves in water. In the case of beryllium, the protective oxide film is very resistant: water does not react with it either during boiling, or even at red heat:

with non-oxidizing acids

All metals of the main subgroup of group II react with non-oxidizing acids, since they are in the line of activity to the left of hydrogen. This forms the salt of the corresponding acid and hydrogen. Examples of reactions:

Be + H 2 SO 4 (dil.) \u003d BeSO 4 + H 2

Mg + 2HBr \u003d MgBr 2 + H 2

Ca + 2CH 3 COOH \u003d (CH 3 COO) 2 Ca + H 2

with oxidizing acids

- diluted nitric acid

All metals of group IIA react with dilute nitric acid. In this case, the reduction products instead of hydrogen (as in the case of non-oxidizing acids) are nitrogen oxides, mainly nitrogen oxide (I) (N 2 O), and in the case of highly dilute nitric acid, ammonium nitrate (NH 4 NO 3):

4Ca + 10HNO 3 ( smashed .) \u003d 4Ca (NO 3) 2 + N 2 O + 5H 2 O

4Mg + 10HNO 3 (badly broken) \u003d 4Mg (NO 3) 2 + NH 4 NO 3 + 3H 2 O

- concentrated nitric acid

Concentrated nitric acid passivates beryllium at ordinary (or low) temperatures, i.e. does not react with it. When boiling, the reaction is possible and proceeds mainly in accordance with the equation:

Magnesium and alkaline earth metals react with concentrated nitric acid to form a wide range of different nitrogen reduction products.

- concentrated sulfuric acid

Beryllium is passivated with concentrated sulfuric acid, i.e. does not react with it under normal conditions, however, the reaction proceeds during boiling and leads to the formation of beryllium sulfate, sulfur dioxide and water:

Be + 2H 2 SO 4 → BeSO 4 + SO 2 + 2H 2 O

Barium is also passivated by concentrated sulfuric acid due to the formation of insoluble barium sulfate, but reacts with it when heated; barium sulfate dissolves when heated in concentrated sulfuric acid due to its conversion to barium hydrogen sulfate.

The rest of the metals of the main IIA group react with concentrated sulfuric acid under any conditions, including cold. Reduction of sulfur can occur to SO 2, H 2 S and S, depending on the activity of the metal, the reaction temperature and the acid concentration:

Mg + H 2 SO 4 ( end .) \u003d MgSO 4 + SO 2 + H 2 O

3Mg + 4H 2 SO 4 ( end .) \u003d 3MgSO 4 + S ↓ + 4H 2 O

4Ca + 5H 2 SO 4 ( end .) \u003d 4CaSO 4 + H 2 S + 4H 2 O

with alkalis

Magnesium and alkaline earth metals do not interact with alkalis, and beryllium easily reacts both with alkali solutions and with anhydrous alkalis during fusion. In this case, when the reaction is carried out in an aqueous solution, water also participates in the reaction, and the products are tetrahydroxoberyllates of alkali or alkaline earth metals and gaseous hydrogen:

Be + 2KOH + 2H 2 O \u003d H 2 + K 2 - potassium tetrahydroxoberyllate

When carrying out a reaction with a solid alkali during fusion, beryllates of alkali or alkaline earth metals and hydrogen are formed

Be + 2KOH \u003d H 2 + K 2 BeO 2 - potassium beryllate

with oxides

Alkaline earth metals, as well as magnesium, can reduce less active metals and some non-metals from their oxides when heated, for example:

The method of reducing metals from their oxides with magnesium is called magnesiumthermia.